The use of manganese dioxide as a cathode material for galvanic cells has long been known in the art. Manganese dioxide exists in several forms, both natural and synthetic. Natural forms of manganese dioxide include ores such as pyrolusite (beta-manganese dioxide), nsutite (gamma-manganese dioxide) and hollandite (alpha-manganese dioxide). Synthetic forms of manganese dioxide include lambda-manganese dioxide (which is produced by acid-treating LiMn.sub.2 O.sub.4 as described in U.S. Pat. Nos. 4,246,253 and 4,312,930), delta-manganese dioxide (made by the chemical reduction of potassium permanganate), and epsilon-manganese dioxide (synthesized by dissolving manganous sulfate in water; adding sufficient sodium hydroxide to precipitate manganous hydroxide and render the solution alkaline; and passing a stream of air or oxygen through the mixture to oxidize the precipitate to manganese dioxide).
These various forms of manganese dioxide are characterized by means of their x-ray diffraction patterns, with each form having a spectrum indicating peaks at various characteristic angstrom spacings.
The electrochemical activity of the various forms of manganese dioxide varies greatly. For example, highly crystalline alpha- and beta- manganese dioxide exhibit poor electrochemical performance in both aqueous and nonaqueous galvanic cells. Other forms of manganese dioxide will function desirably in certain types of cells or for certain uses only. For example, lambda-manganese dioxide when employed in nonaqueous electrolyte cells demonstrates a multistep discharge curve with a relatively high initial voltage. While this type of discharge is suitable for cell usages which require such a high initial output, such voltage may be too high for several other cell usages. Consequently, it would be advantageous to provide a novel form of manganese dioxide which exhibits desirable electrochemical activity.
Accordingly, it is an object of this invention to provide a novel form of manganese dioxide which exhibits desirable electrochemical activity.
It is a further object of this invention to provide a process for the manufacture of such novel form of manganese dioxide.
It is yet a further object of this invention to provide a galvanic cell employing such novel manganese dioxide as cathode material.
The foregoing and additional objects will become more fully apparent from the following description and examples and the accompanying drawing.